"4 seconds" - remember that magical number ? If a web page doesn't load within 4 seconds, lot of visitors are likely to leave the website.

Related: Tricks to Make Your Webpages Load Faster

Now several elements of a web page (like CSS, Iframes, Flash, Javascript, graphics) can increase the page loading time but how do you pinpoint the exact culprit that slowing the site?

A normal HTML web page may have ad scripts being served from Google Adsense servers, Flash video player from YouTube, images from Blogger Photos and so on.

WebPageTest is a useful tool that mimics a web browser and generates a nice interactive graph detailing the load time of different objects (like CSS Files, Javascript, etc) which are included in the web page.

You can view the list of objects either in load order or as a hierarchy. The hierarchy view allows you to see which objects are linked to in for example a CSS file. Objects that fail to load are highlighted in red.

See: Test the Speed and Performance of your Website